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2 Skeletal MuscleMovements of our body are accomplished by contraction of the skeletal musclesFlexion: contraction of a flexor muscle draws in a limbExtension: contraction of extensor muscleSkeletal muscle fibers have a striated appearanceSkeletal muscle is composed of two fiber types:Extrafusal: innervated by alpha-motoneurons from the spinal cord: exert forceIntrafusal: sensory fibers that detect stretch of the muscleAfferent fibers: report length of intrafusal: when stretched, the fibers stimulate the alpha-neuron that innervates the muscle fiber: maintains muscle toneEfferent fibers: contraction adjusts sensitivity of afferent fibers.8.2

3 Skeletal Muscle AnatomyEach muscle fiber consists of a bundle of myofibrilsEach myofibril is made up of overlapping strands of actin and myosinDuring a muscle twitch, the myosin filaments move relative to the actin filaments, thereby shortening the muscle fiber8.3

4 Neuromuscular JunctionThe neuromuscular junction is the synapse formed between an alpha motor neuron axon and a muscle fiberEach axon can form synapses with several muscle fibers (forming a motor unit)The precision of muscle control is related to motor unit sizeSmall: precise movements of the hand (e.g., fingers, 1:<10)Large: movements of the leg (e.g., 1:>300)ACh is the neuromuscular junction neurotransmitterRelease of ACh produces a large endplate potentialVoltage changes open CA++ channelsCA++ entry triggers myosin-actin interaction (rowing action)Movement of myosin bridges shortens muscle fiber8.4

5 Smooth and Cardiac MuscleSmooth muscle is controlled by the autonomic nervous systemMultiunit smooth muscle is normally inactiveLocated in large arteries, around hair and in the eyeResponds to neural or hormonal stimulationSingle-unit smooth muscle exhibits rhythmic contractionMuscle fibers produce spontaneous pacemaker potentials that elicit action potentials in adjacent smooth muscle fibersSingle-unit muscle is found in gastrointestinal tract, uterus, small blood vesselsCardiac muscle fibers resemble striated muscle in appearance, but exhibit rhythmic contractions like that of single-unit smooth muscle8.5

8 Spinal Cord ReflexesMonosynaptic reflexes involve a single synapse between a sensory fiber from a muscle and an alpha-motor neuronSensory fiber activation quickly activates the alpha motor neuron which contracts muscle fibersPatellar reflexMonosynaptic stretch stretch (posture)Polysynaptic reflexes involve multiple synapses between sensory axons, interneurons, and motor neuronsAxons from the afferent muscle spindles can synapse ontoAlpha motoneuron connected to the agonist muscleAn inhibitory interneuron connected to the antagonist muscleSignals from the muscle spindle activate the agonist and inhibit the antagonist muscle8.8

9 Polysynaptic Reflex 8.9 Dualism-mind is separate from the bodyDescartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.The pineal gland is where the soul controls the physical bodyMonism: the belief that the mind is the working of the body (no need for a separate soul.Determinism-the notion that mental states are produced by physical mechanisms.Reductionists-we break complex phenomena into less complicated sytems.8.9

11 Motor “Homunculus” 8.11 Dualism-mind is separate from the bodyDescartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.The pineal gland is where the soul controls the physical bodyMonism: the belief that the mind is the working of the body (no need for a separate soul.Determinism-the notion that mental states are produced by physical mechanisms.Reductionists-we break complex phenomena into less complicated sytems.8.11

12 Cortical Control of MovementDualism-mind is separate from the bodyDescartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.The pineal gland is where the soul controls the physical bodyMonism: the belief that the mind is the working of the body (no need for a separate soul.Determinism-the notion that mental states are produced by physical mechanisms.Reductionists-we break complex phenomena into less complicated sytems.8.12

14 Corticospinal TractNeurons of the corticospinal tract terminate on motor neurons within the gray matter of the spinal cordCorticospinal tract starts in layer 5 of primary motor cortexPasses through the cerebral peduncles of the midbrainCorticospinal neurons decussate (crossover ) in the medulla80% become the lat. corticospinal tract20% become the ventral corticospinal tractTerminate onto internuncial neurons or alpha-motoneurons of ventral hornCorticospinal tracts control fine movementsDestruction: loss of muscle strength, reduced dexterity of hands and fingersNo effect of corticospinal lesions on posture or use of limbs for reaching8.14

15 The ApraxiasApraxia refers to an inability to properly execute a learned skilled movement following brain damageLimb apraxia involves movement of the wrong portion of a limb, incorrect movement of the correct limb part, or an incorrect sequence of movementsCallosal apraxia: person cannot perform movement of left hand to a verbal request (anterior callosum interruption prevents information from reaching right hemisphere)Sympathetic apraxia: damage to anterior left hemisphere causes apraxia of the left arm (as well as paralysis of right arm and hand)Left parietal apraxia: difficulty in initiating movements to verbal requestConstructional apraxia is caused by right parietal lobe damagePerson has difficulty with drawing pictures or assembling objectsDualism-mind is separate from the bodyDescartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.The pineal gland is where the soul controls the physical bodyMonism: the belief that the mind is the working of the body (no need for a separate soul.Determinism-the notion that mental states are produced by physical mechanisms.Reductionists-we break complex phenomena into less complicated sytems.8.15

16 The Basal GangliaBasal ganglia consist of the caudate nucleus, the putamen and the globus pallidusInput to the basal ganglia is from the primary motor cortex and the substantia nigraOutput of the basal ganglia is toPrimary motor cortex, supplemental motor area, premotor cortexBrainstem motor nuclei (ventromedial pathways)Cortical-basal ganglia loopFrontal, parietal, temporal cortex send axons to caudate/putamenCaudate/putamen projects to the globus pallidusGlobus pallidus projects back to motor cortex via thalamic nucleiDualism-mind is separate from the bodyDescartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.The pineal gland is where the soul controls the physical bodyMonism: the belief that the mind is the working of the body (no need for a separate soul.Determinism-the notion that mental states are produced by physical mechanisms.Reductionists-we break complex phenomena into less complicated sytems.8.16

17 Anatomy of the Basal GangliaDualism-mind is separate from the bodyDescartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.The pineal gland is where the soul controls the physical bodyMonism: the belief that the mind is the working of the body (no need for a separate soul.Determinism-the notion that mental states are produced by physical mechanisms.Reductionists-we break complex phenomena into less complicated sytems.8.17

19 Huntington’s DiseaseHuntington’s disease (HD) involves uncontrollable, jerky movements of the limbsHD is caused by degeneration of the caudate nucleus and putamenCell loss involves GABA-secreting axons that innervate the external division of the globus pallidus (GPe)The GPe cells increase their activity, which inhibits the activity of the subthalamic nucleus, which reduces the activity level of the GPi, resulting in excessive movementsHD is a hereditary disorder caused by a dominant gene on chromosome 4This gene produces a faulty version of the protein huntingtinDualism-mind is separate from the bodyDescartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.The pineal gland is where the soul controls the physical bodyMonism: the belief that the mind is the working of the body (no need for a separate soul.Determinism-the notion that mental states are produced by physical mechanisms.Reductionists-we break complex phenomena into less complicated sytems.8.19

20 The CerebellumCerebellum consists of two hemispheres with associated deep nucleiFlocculonodular lobe is located at the caudal aspect of the cerebellumThis lobe has inputs and outputs to the vestibular systemInvolved in control of postureVermis is located on the midline of the cerebellumReceives auditory and visual information from the tectum and cutaneous information from the spinal cordVermis projects to the fastigial nucleus which in turn projects to the vestibular nucleus and to brainstem motor nucleiDamage to the cerebellum generally results in jerky, erratic and uncoordinated movementsDualism-mind is separate from the bodyDescartes believed that the pineal body directed fluid from the ventricles into the holow fibers we call nerves-this induced muscle action.The pineal gland is where the soul controls the physical bodyMonism: the belief that the mind is the working of the body (no need for a separate soul.Determinism-the notion that mental states are produced by physical mechanisms.Reductionists-we break complex phenomena into less complicated sytems.8.20